Up to 2 million Muslims from around the world have arrived in Saudi Arabia for the annual hajj pilgrimage amid a diplomatic war of words between the Saudi regime and the Iranian government over last year’s disaster.

More than 2,400 pilgrims were crushed to death in 2015, and some fear a repeat despite fresh security measures for the hajj, which begins on Friday and lasts five days. More than 27,000 security personnel will be deployed around the holy sites at Mecca and Medina.

A huge increase in international pilgrims over recent decades has increased pressure on the holy sites of Mecca and Medina, and the infrastructure needed to cope with a massive influx of people.

Pilgrims are required to travel in organised groups, and a Saudi official has said that those caught trying to enter the holy sites without a permit will be tried and sentenced within 24 hours.

“Verdicts of imprisonment and fines against illegal pilgrims will be issued within 24 hours,” said Muhammad al-Anzi, the director of the department of expatriates in the directorate general of prisons, Al Arabiya reported.

Rulings will be issued by special administrative committees stationed at checkpoints along the roads leading to Mecca and other holy sites, and violators will be sent to a detention centre within 48 hours, Anzi said. All verdicts will be final, he added.

Earlier this week, Iran’s supreme leader, Ayatollah Ali Khamenei repeated his claim that Iranian pilgrims had been “murdered” by the Saudi regime during last year’s hajj, blaming the deadly crush on incompetence. The Iranian government urged Muslims to unite against Saudi Arabia.

The Saudis “have made the divine sanctuary unsafe for everybody”, Khamenei said in a statement posted on his website. “The heartless and murderous Saudis locked up the injured with the dead in containers – instead of providing medical treatment and helping them or at least quenching their thirst. They murdered them.”

Ayatollah Ali Khamenei attends a meeting with survivors of the hajj crush in Tehran on Wednesday. Photograph: Uncredited/AP

He added: “Those who have reduced Hajj to a religious tourist trip and have hidden their enmity and malevolence towards the faithful and revolutionary people of Iran under the name of ‘politicising hajj’, are themselves small and puny satans who tremble for fear of jeopardising the interests of the great satan, the US.”

The Saudi grand mufti, Sheikh Abdulaziz al-Sheikh, responded by saying Iran’s leaders were not Muslims, but descendants of the Magi, or Zoroastrians. “Their hostility towards Muslims is ancient.”

More than 400 Iranians were killed in the crush, exacerbating tensions between the two countries already at breaking point over the wars in Syria and Yemen. For the first time in almost three decades Iranians will not join this year’s pilgrimage.

According to the Saudi government, 769 pilgrims were killed at Mina when two huge groups of people converged on 24 September. It was the worst hajj disaster since 1990, when 1,426 people were suffocated and trampled to death in a tunnel.

Losing ground, fighters and morale – is it all over for Isis?

Read more

However, a report by the Associated Press found that 36 countries reported a total of 2,411 deaths in last year’s disaster – three times the number acknowledged by the Saudis. Among the dead, the biggest group was from Iran. Mali claimed 305 dead, Nigeria 274, Egypt 190, and Bangladesh 137.

King Salman ordered an inquiry into the disaster, which came 13 days after 111 people were killed when a crane collapsed at the Grand Mosque in Mecca, but few details have been made public.

Pilgrims are being issued with electronic bracelets in an attempt to monitor and control crowd flow. The bracelets also contain medical and personal identification details. More than 1,000 security cameras have been put in place and security and emergency forces have carried out practice drills.

About 25,000 pilgrims from the UK are expected to be in Mecca. In July, the Association of British Hujjaj (Pilgrims) launched a health and safety awareness campaign, which highlighted the risks of infectious diseases, such as meningitis and coronavirus, as well as the dangers of stampedes and crushes.

“Authorities from around the world must learn lesson from last year’s hajj disasters and to set up strategy to help and protect hajj pilgrims in order to protect them from becoming casualties in any future hajj tragedy,” said Khalid Pervez, the association’s general secretary.

The hajj is one of the five pillars of Islam, and able-bodied Muslims are expected to make the pilgrimage at least once in their lives.

The rituals include the tawaf: circling the holy Kaaba at the centre of the Grand Mosque seven times in an anticlockwise direction while repeating prayers. In the valley of Mina, pilgrims hurl stones at pillars symbolising the devil. All pilgrims wear the same simple white robes, called thram.

The dates of the hajj depend on the lunar calendar, and move forward each year. For the next 10 years the hajj will take place in the summer months, when temperatures at the holy sites can exceed 40C (104F), increasing the risk of dehydration and heat exhaustion.